1. Field of the Invention
The present invention is directed to an apparatus and method for three-dimensional reconstructions of tortuous vessels, and in particular, to three-dimensional reconstructions of tortuous vessels such as coronary arteries generated from stacked intravascular ultrasound (IVUS) ECG-gated segmented IVUS frames of a pullback sequence combined by data fusion with biplane angiography.
2. Background of the Related Art
Selective coronary angiography is one related art catheter-based imaging technique used for the diagnosis of coronary artery disease. Coronary contrast angiograms are X-ray projections of the contrast bolus inside the vessel lumen. However, due to the projective nature of angiography, the cross-sectional shape of the lumen remains unknown. Moreover, plaque is visualized only indirectly as reduction of lumen diameter, and vessel wall as well as surrounding tissue (adventitia) are not imaged at all. Disadvantageously, even in two projections, the cross-sectional shape of the stenosis can be only roughly estimated. However, biplane angiography allows for accurate reconstruction of the three-dimensional (3D) course of the vessel centerline.
Another related art imaging technique for qualitative and quantitative assessment of coronary arterial wall and plaque is intravascular ultrasound (IVUS) using a catheter or the like. IVUS offers well-calibrated cross-sectional views of coronary morphology (i.e., lumen, plaque, wall, adventitia). Amount and composition of plaque at local stenosis may be quantitatively analyzed through a catheter pullback and even small amounts of plaque are depicted in diffusely deceased arteries. Disadvantageously, IVUS lacks information regarding the 3D vessel geometry.
In the area of IVUS, an increasing number of today's commercially available imaging systems support the generation of pseudo 3D reconstructions. Possible ECG-gated frames of IVUS pullback sequence are stacked up resulting in a straight vessel reconstruction. Clearly, this method is not able to accurately represent the tortuosity of a coronary artery, and it does not account for the twist and the motion of the catheter during pullback.
The potential of the two techniques to complement each other is based on the information provided in their inherent image characteristics. Further, although IVUS examinations can be preceded, guided and/or followed by coronary contrast angiography, both techniques can acquire images during cardiac catherization. Automated segmentation and quantification methods are available for contrast arteriograms as well as for IVUS images.
To overcome limitations of each imaging technique for accurate 3D reconstruction of tortuous coronary arteries, data fusion between biplane angiography and IVUS pullback imaging is used to derive a spatially correct and clinically useful vessel reconstruction by combining the complementary strengths of both imaging techniques. The 3D course of the pullback path is first derived from biplane angiograms and then fused with the segmented IVUS images of the pullback image sequence. The goal is a 3D vessel reconstruction that is both anatomically complete and geometrically correct so that bendings of the vessel are represented in the reconstruction and plaque is located rotationally correct.
The basic concept of fusion-based 3D reconstructions is illustrated in FIG. 1. The segmented cross sections of an IVUS pullback sequence 100 (left) segmented into lumen, plaque and vessel wall are mapped to the corresponding vessel centerline of the 3D coronary tree vessel segment 110 (right) reconstructed from a biplane contrast angiogram. As discussed in "Semi-automated Segmentation and 3D Reconstruction of Coronary Tree: Biplane Angiography and Intravascular Ultrasound Data Fusion" by G. Prause et al., Proceedings of the Conference on Medical Imaging, Feb. 11-15, 1996 (hereafter Prause et al.) the contents of which are incorporated by reference, the processing steps break down into image acquisition, tree reconstruction, border detection, mapping, and evaluation. Image acquisition includes injecting radiopaque dye into the examined coronary tree and the heart is imaged with a calibrated biplane X-ray system before IVUS pullback. Tree reconstruction includes constructing the 3D centerline of the coronary tree from the geometrically corrected biplane angiograms using an automated segmentation method and manual matching of corresponding branching points. Border detection includes automatically determining the vessel wall and plaque in the acquired IVUS pullback images. During mapping, the IVUS cross-sections are mapped perpendicular to the vessel centerline, the twist of the IVUS catheter is calculated and the vessel reconstruction is rotationally adjusted. Evaluation includes visually and quantitatively analyzing the reconstructed coronary tree and vessel segment.
In the related art techniques, problems arise with data fusion between biplane angiography and IVUS pullback imaging including the definition of the pullback path. Further, several sources of error have been reported that may impede the accuracy of the 3D vessel reconstruction. Most of these errors appear either fully within the IVUS modality or within the angiography modality. These problems include significant processing demands with disjointed 2D IVUS cross-sections and how to position IVUS slices in a vertex area.
In addition to the above, a line object (e.g., an intravascular ultrasound catheter inserted in a coronary vessel) is visualized using two projection images. The goal is to obtain 3D information about the line object (catheter). The related art approach is to independently determine the line object projection in the two projection images and perform their 3D reconstruction according to the calibrated epipolar geometry of the projection acquisition system. Due to projection image ambiguities that are inherent to projection imaging, such an approach may result in reconstructions that are infeasible. For example, ambiguities of the projections if considered independently in individual projections can lead to line object reconstructions having a shape that cannot be physically achieved by the original line object. Thus, the related art apparatus and methods result in 3D reconstructions that cannot happen in actuality (e.g., including excessive bending, sharp corners, etc.).